I had a C'Dale Jekyll that cracked at the seatpost. I had it welded by an experienced aluminum welder and then I had it heat treated, quenched and baked to bring it back to T6 temper. It cost about $375, but my wife loves the bike! It has been perfect since.

I know this sounds like a weird suggestion, but composites could probably fix it. Carbon and fiberglass are surprisingly not too difficult to work with, and I've seen it repair a cracked seat tube on an aluminum frame. Seems it may be more difficult to bond right there, and it would look different after it's all done because of the layers of carbon or fiberglass.

If it was 7005 it would be $400 for a new headtube
With 6061 you're looking at $400 plus another couple of hundred bucks to bring it through heattreat and a general pain in the ass.
You'll lose your sweet burnished finish too.
Find a new one. Those things were everywhere.